1 files changed, 42 insertions, 0 deletions
diff --git a/src/features/plugins/logic/cascade.ts b/src/features/plugins/logic/cascade.ts
new file mode 100644
index 0000000..0cc6834
--- /dev/null
+++ b/src/features/plugins/logic/cascade.ts
@@ -0,0 +1,42 @@
+import type { PluginNode } from "./types";
+
+/**
+ * The transitive set of LOADED dependents that would also be unloaded if
+ * `targetId` were unloaded — the §8 cascade-uncheck warning's list ("unloading
+ * X also unchecks Y, Z"). Client mirror of the backend's
+ * `computeUnloadCascade` (plan 05): the reverse-dependency closure computed
+ * over the LOADED subgraph only (an unloaded intermediate breaks the chain —
+ * a loaded dependent behind it is already unmet and is not part of THIS
+ * cascade). The server still enforces the real cascade; the FE computes the
+ * same set to warn before the request goes out.
+ *
+ * Pure input → output; deterministic order (alphabetical by id) so tests and
+ * renderings are stable.
+ */
+export function computeCascade(targetId: string, nodes: readonly PluginNode[]): readonly string[] {
+  // Reverse edges within the loaded subgraph: dep id → loaded dependent ids.
+  const dependentsOf = new Map<string, string[]>();
+  for (const node of nodes) {
+    if (!node.loaded) continue;
+    for (const dep of node.dependsOn) {
+      const list = dependentsOf.get(dep);
+      if (list) list.push(node.id);
+      else dependentsOf.set(dep, [node.id]);
+    }
+  }
+
+  // BFS over reverse edges, collecting every reached loaded dependent.
+  const out: string[] = [];
+  const seen = new Set<string>([targetId]);
+  const queue = [targetId];
+  while (queue.length > 0) {
+    const current = queue.shift() as string;
+    for (const dependent of dependentsOf.get(current) ?? []) {
+      if (seen.has(dependent)) continue;
+      seen.add(dependent);
+      out.push(dependent);
+      queue.push(dependent);
+    }
+  }
+  return out.sort((a, b) => a.localeCompare(b));
+}